Many electronic or computerized devices and equipment, regardless of size, are a managed interconnection of many different subsystems. Such electronic computing equipment (e.g. disk arrays, computers, routers, switches) utilize a shared copper conductor crossbar switch or bus backplane for interconnecting the subsystem components (e.g. processors, cache, shared memory, disk controllers, host interface cards). Although the copper crossbar switch provides a substantial advance in throughput ability, it typically has limitations regarding expandability, reliability, and the ability to multicast or eavesdrop between the subsystems. A typical copper crossbar or bus backplane may allow approximately 4-8 simultaneous and separate data paths.
Computing systems and peripherals typically consist of several cards or blades plugged into a chassis. These cards are generally interconnected by a common backplane, which is typically copper, and/or a small number of shared buses. The sharing of busses has typically been an architectural bottleneck that has limited the maximum throughput of the computer or peripheral. Because the busses are shared, any particular conversation or communication between two interconnected components, such as between a disk director and a channel processor, for example, must wait its turn. This connection method architecturally limits the amount of data that can be moved by the computing device.
In order to improve on the limitations of shared busses, crossbar switches that increased the interconnectability and throughput for a backplane connection were developed. Crossbar switches are generally not limited in the same manner as the shared-bus architecture because a crossbar switch typically allows a certain number of separate data transmissions to take place simultaneously, without any one transmission interfering with (or holding off) another. For example, in an 8×8 crossbar switch, up to 8 separate data transmissions may take place simultaneously. This architecture allows a much higher total system throughput rate.
While shared busses and crossbar switches generally allow for multiple interconnections of multiple electronic computer sub-systems, there are problems and limitations with the current shared bus and crossbar switch technology. Because the interconnection paths of shared busses and crossbars are typically hard-wired, it is impractical, without substantial re-design and retrofitting or even total replacement, to expand the capacity of the bus or crossbar.
Current bus and crossbar technology does not typically allow for multicasting (i.e., communicating data to more than one receiving component and/or subsystem on the same transmission) or eavesdropping (i.e., one subsystem that taps into the data communication path between two other subsystems in order to perform some other function). Furthermore, crossbar switches are generally quite complex, which results in a high expense. This expense greatly increases when attempting to scale and/or expand the connectability and/or throughput of the backplane.
In such conventional, copper crossbar or backplane systems, the abundance of long, parallel copper wires (like antennae) may also create substantial Radio Frequency Interference (RFI). RFI may produce unwanted effects, such as: (1) adding expense in terms of the time/money to mitigate or alleviate the interference; (2) limiting how closely devices can be racked together; and (3) creating the potential for unwanted eavesdropping. Furthermore, RFI may pose a health risk because of the electromagnetic field generated by the RF signals.